Total Organic Carbon (TOC ) of the surface layer sediments covering the seafloor of the Romanian Black Sea coast (original) (raw)
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The Nature of Organic Matter in the Danube River Particles and North-western Black Sea Sediments
Estuarine, Coastal and Shelf Science, 2002
Suspended matter and sediments from the Danube River and the adjacent north-western Black Sea were analysed for organic carbon, nitrogen and biogenic carbonate and silica, as well as for different fractions of organic matter such as amino acids and carbohydrates. In addition, the nitrogen isotopic composition of surficial sediments of the NW Black Sea was examined. Particulate organic carbon (POC)
Frontiers in Marine Science, 2024
It is essential to determine the concentrations of metals/metalloids in marine sediments and their contamination status to develop appropriate pollution control strategies and/or improve existing ones. Spatial distribution of aluminum (Al) and some trace elements, i.e., arsenic (As), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn), accumulated in surface sediments of the northwestern (NW) Black Sea (Romanian zone) was evaluated. Sediment samples were collected in 2019 from 32 stations located at water depths in the range of 12.7-149 m. The mean values ± standard deviations (SD) of element concentrations were as follows: 3.9 ± 1.6% for Al, 11.2 ± 10.2 mg/ kg for As, 64.8 ± 27.0 mg/kg for Cr, 32.7 ± 15.0 mg/kg for Cu, 0.10 ± 0.09 mg/kg for Hg, 45.3 ± 23.8 mg/kg for Ni, 24.6 ± 9.6 mg/kg for Pb, and 68.0 ± 28.0 mg/kg for Zn. These values are not significantly different (p > 0.05) from those found in a previous study on surface sediments collected in 2018 from 22 stations located in the same area, but at lower water depths (13.5-67 m). Contamination factor (CF) was used to assess the contamination status of surface sediments. The mean values of CF (0.26-1.23) reveal low to moderate contamination with Pb and low contamination with the other elements. Principal component analysis (PCA) and correlation analysis indicated that As, Cu, Ni, Hg, Pb, and Zn were associated with clay, silt, and organic matter, suggesting that these elements mainly came from the Danube discharges and also from local anthropogenic sources, whereas Al, Cr, and partly Hg, Pb, and Zn originated from rock/soil weathering and erosion. The concentration levels of As, Cu, Hg, Ni, Pb, Zn, TOC, silt, and clay were higher in sediments collected from stations generally located at higher water depths (up to 118 m), suggesting that the TEs associated with the finer carriers were transported offshore by currents and waves, whereas the concentration levels of Al, Cr, Hg, and Zn were higher in sediments with lower levels of CaCO 3 content (10.1-24.3%), collected from shallower stations (water depths of 12.7-42.0 m).
The assessment of the current nutrient levels and eutrophication of the Romanian Black Sea waters, as part of the Marine Strategy Framework Directive implementation, was based on data acquired during 2006-2011 from the monitoring network stations consisting of 36 stations along the Romanian littoral. Additionally, were collected daily (for chemistry) and bi-weekly (for phytoplankton) data from the Constan’a station. The trends were analyzed based on historical data (1964/1980-2011) from the East Constanța transect. The inorganic phosphorus content is influenced by the Danube’s and WWTPs’ input. Due to different flows, the fluvial input is more significant. On the long-term, decreased concentrations compared to the values of the 1960s, reference period for the good quality of the Romanian Black Sea waters, were observed. These low values give to phosphorus the feature of a limitative element for the phytoplankton’s proliferation. The inorganic nitrogen content is mainly influenced by the Danube’s input. Seasonally and on a restricted area, we found in the neighborhood of WWTPs higher ammonia concentrations. On the long-term, we observed the decreasing concentrations up to the level of 1991-1992, when the intensity of the eutrophication started to drop. Therefore, the intensity and number of the monospecific blooms have decreased, the mixed blooms phenomena and the increasing diatoms proportion in the phytoplanktonic populations occurred and, consequently, the eutrophication has been slightly reduced. Dinoflagellates’ proportion was reduced, but still, in the summer, they can reach 40% from the total phytoplankton. Thus, the ecosystem recovery is still fragile and could be easily destabilized by the influence of the anthropogenic pressures and climate changes. KEYWORDS: nutrients, eutrophication, Danube, Black Sea
Assessment of Water Quality at the Romanian Black Sea Shore
2013
Over the last 40 years the Black Sea recorded a serious degradation of the aquatic ecosystem, mainly due to human pollution. Excessive nutrients concentration in water mass (from agriculture or sewage treatment) caused the apparition of eutrophication in Black Sea. Eutrophication disturbs the aquatic ecosystems and become a risk to organisms that depend on water resource and also to human health. The occurrence of eutrophication phenomenon in the Black Sea produces big economic losses in tourism and fishing industry. This study investigates, based on experimental observations, the causes and effects of eutrophication occurrence. Furthermore, based on current state of eutrophication indicators in the sea water, this paper tried to identify possible methods of rehabilitation of the marine ecosystem.
2015
Abstract. The paper presents a part of the scientific activity of GEOECOMAR team during the IAEA project RER 2/003 Marine Environmental Assessment of the Black Sea Region, on board of R/V “Prof. Vodyanitskyi ” and in laboratories. The Black Sea presents different sedimentological and geochemical characteristics in the eastern and western sub-basins. Whole sections of the Upper and Middle Holocene sediments were revealed in most cores recovered from the whole Black Sea basin. Scientific methods (grain size, X ray investigations, rate of sedimentation and radiogenic measurements, geochemistry characteristics of water and sediments) showed the general distribution of the bottom sediments, at the surface and downward, syn- and postdepositional sedimentary structures, lithological and geochemical compositions. As a result of detailed sedimentological studies in the whole Black Sea basin, for the first time a complete picture of the current grain size composition in the Upper Holocene sed...
Estuarine Coastal and Shelf Science, 2002
The mixing zone between the Danube and the Black Sea was investigated at the front of the Chilia and Sulina branches of the Danube delta, in April-May 1997, during two periods corresponding to conditions at the end of winter (Chilia and Sulina branches) and the beginning of spring (Sulina branch). The distribution of the organic matter in the particulate, colloidal and truly dissolved pools along the salinity gradient was characterized at both global and molecular levels using biochemical parameters. The distribution of particulate organic carbon (POC) paralleled that of total suspended matter in winter, whereas decoupling was observed in spring, reflecting active biological mechanisms in the mixing zone off the Sulina branch during this period. This is supported by distribution patterns of polyunsaturated fatty acids (PUFA) and branched fatty acids (BrFA), which are indicators of phytoplankton and bacteria activities, respectively. The 13 C isotopic signature of POC in the Danube-Black Sea mixing zone varied of between 29·1 and 24·6‰, which is consistent with the usual temperate range of estuarine systems. In spring, the observed shift towards lower values in the area of salinity 0-5 suggested a gradual change in the composition of POC, such as that caused by cell lysis of riverine planktonic populations induced by a salinity increase. A subsequent increase of 13 C values towards higher salinities indicated phytoplankton growth in the estuarine/marine zone, as assessed by high concentrations of PUFA. Indirect evidence of sedimentation of terrestrial particles in the upper part of the salinity gradient in the range of 2-3 was suggested by the decrease of the content of particles and POC in fatty acids (C 24 -C 32 ) and n-alkanes (C 25 -C 35 ), both constituents of cuticular waxes of higher plants. A tight coupling was suggested between phytoplankton and bacteria by similar distributions of PUFA and BrFA along the salinity gradient. The distribution of dissolved organic carbon (DOC) varied according to the season. In spring, the DOC concentrations remained constant across the salinity gradient in front of the Sulina branch at about 2·7 mg l 1 , whereas higher concentrations, >4 mg l 1 , were observed in winter at stations located in the low salinity (2-4 and 5-8) area. A few data were obtained for 13 C of the DOC pool, with an average of 26·9‰ in the Danube River end-member and values close to those of POC off the various branches. The low molecular weight (LMW) fraction of DOC isolated from water by sequential cross-filtration was evaluated by summing the pool of the combined and free amino acids and that of the combined and free carbohydrates. The distribution of LMW DOC along the salinity gradient was similar in the three investigated areas. Off the Sulina branch, proportions of LMW DOC fluctuated between 17 and 37‰ in winter and between 23 and 35‰ in spring. Two zones of high LMW DOC were located in two ranges of salinity-between 2 and 4 and between 5 and 8-probably originating from the release of decaying diatoms, assessed by high molecular proportions of serine in the combined amino acids. LMW DOC indicated a high potential for microbal activity, as shown by concomitant distributions of branched fatty acids.
Global Biogeochemical Cycles, 1994
Sedimentologic and geochemical studies of box and gravity cores recovered from the Black Sea during the first leg of a multileg international Black Sea expedition in 1988 allow reconstruction of the basinwide Holocene environmental history of the Black Sea. In the deeper parts of the basin, box cores typically recovered a flocculent surface layer ("fluff"), laminated coccolith marls of Unit I (25-45 cm thick), and the upper 5-10 cm of finely laminated, darkcolored sapropels of Unit II. Fine-grained, homogeneous mud turbidites are interbedded with Units I and II over much of the basin, but the stratigraphic position of these turbidites differs from site to site. The deposition of individual turbidites up to 15 cm thick does not appear to have significantly disturbed underlying laminae. Sediment trap deployments in the Black Sea suggest that light and dark laminae couplets represent annual increments of sedimentation (i.e., varves); we have therefore constructed a varve chronology for the sequence in order to correlate and date distinctive sedimentation and paleoenvironmental events. Distinctive groups of laminae in Unit I can be correlated across the entire deeper basin (a distance of more than1000 km). This implies a remarkable homogeneity in production, accumulation, and preservation of biogenic material over much of the Black Sea during deposition of Unit I. The change from deposition of finely laminated, organic carbon-rich sapropels (Unit II) to laminated, more calcareous, coccolithrich marls (Unit I) is thought to represent the crossing of a salinity threshold for Emiliania huxleyi. The varve chronology sets this change at about 1.63 ka (1633+100 yr B.P.), but the record of magnetic secular variation measured in several cores produces an age estimate of about 2.0 ka for the base of Unit I, or about 1.2 times the varve age. The average of six calibrated accelerator mass spectrometry radiocarbon ages for the base of Unit I is 2.7 ka, or about 1.7 times the varve age. Following the initial change to coccolith-dominated sedimentation, deposition of sapropel resumed for at least one significant period, 1.56-1.25 ka. Since 1.25 ka, cycles of carbonate deposition with quasi-decadal periodicities have produced characteristic darker and lighter assemblages of laminae. These cycles may have been climatically driven. Geochemical analyses coupled with the varve ages adopted herein indicate that accumulation rates of carbonate are nearly an order of magnitude higher in Unit I (averaging 35-45 g m '2 yr -•) than in sapropelic Unit II, which contains primarily detrital carbonate. The accumulation of lithogenic components in parts of Unit I is only 1.5 times the rate in Unit II. Deepwater organic carbon accumulation rates are somewhat higher in Unit I (3.5-4.5 g m-2yr '•) than in the upper part of Unit II. Organic carbon accumulation rates in Unit I are somewhat antithetic to those of carbonate, and on the basis of this and additional constraints placed by pyro!ysis and carbon isotopic analyses of organic material, it appears that terrestrial organic matter is an important component (perhaps >25%) of total organic carbon burial in the basin. Unit I in the western part of the Black Sea has a higher terrestrial organic component and higher accumulation rates of terrigenous clastic material than Unit I in the eastern part. This difference between eastern and western Black Sea is to be expected because of the major rivers that empty into the western Black Sea from eastern Europe, Ukraine, and Russia. Shallow slope sites, but still within euxinic bottom waters, have lower organic carbon accumulation rates and lower pyrolysis hydrogen indices than deepwater basinal sites, suggesting selective resuspension and oxidation of organic matter at basin margins and focusing of organic matter deposition toward the basin center. A comparison of the Black Sea data with those from several open ocean sites with similar water depths showed no significant difference between organic carbon accumulation rates under oxic and anoxic conditions. For a given bulk accumulation rate the organic carbon accumulation rates, normalized to primary productivity, are about the same in both settings.
2000
A positive correlation between the finer grain size fractions (clay and/or silt) and TOC was well established long ago (Buchanan and Longbottom, 1970; Mayer, 1994; Tyson, 1995 etc.). The close association of the two components is probably explained by both the capacity of the finer particles to hinder the diffusion of the oxygen into the sediments, thus favoring the preservation of organic matter and the adsorp-tion of organic particles onto the charged surfaces of the clay minerals. The last process largely depends upon the specific surface of the sediment, so much so that sometimes this parameter is preferred over the percentage of finer fractions as independent variable, determining the TOC concentration in sediments. Of course there is not a unique, generally valid relation. There are important local variations, determined mainly by the local primary production, sedimentary rates and oxygen regime in the water column and sediments. The mathematical relation between the percentag...
Transport and fate of Danube Delta terrestrial organic matter in the Northwest Black Sea mixing zone
Marine Chemistry, 2002
Within the framework of the European project EROS 21, a biogeochemical study of particles transported from the Danube Delta to the Northwestern Black Sea whose carbon cycle is dominated by riverine inputs was carried out in spring off the Sulina branch of the Danube Delta. The distribution of particulate organic carbon (POC), chlorophyll a (Chl a), C/N, and d 13 C evidenced an omnipresent contribution of terrestrial organic matter throughout the study area together with a dilution of these inputs by freshwater and marine organisms. Four lipid series, n-alkanoic acids, n-alkanes, n-alkanols, and sterols were analyzed by gas chromatography and gas chromatography/mass spectrometry. Several signature compounds were selected to delineate dispersion of terrestrial organic carbon: (1) long-chain n-alkanoic acids in the range C 24 -C 34 , long-chain n-alkanes in the range C 25 -C 35 , long-chain n-alkanols in the range C 22 -C 30 , 24-ethylcholesta-5,22-dien-3h-ol (29D 5,22 ) and 24-ethylcholesterol (29D 5 ) for vascular plant-derived material and (2) coprostanol (27D 0,5h ) for faecal contamination associated with sewage effluents. A marked decrease was observed between the concentrations of different vascular plant markers characterizing the two end members: riverine at salinity 0.3 and marine at salinity 15.5. The decrease observed for marine/riverine end members (expressed as a function of organic carbon) varied in a large range, from 4% for n-alkanes to 18.6%, 20.4% and 24% for n-fatty acids, n-alkanols and sterols, respectively. These values reflect a combination of various processes: size-selective particle sedimentation, resuspension of different particle pools of different sizes and ages, and/or selective biological utilization. The multi-marker approach also suggested the liberation in the mixing zone of terrestrial moieties, tightly trapped in macromolecular structures of the riverine material. The greatest decrease for marine/riverine end members was observed for coprostanol (0.9%), underlining the efficiency of the mixing zone as a sink for sewage-derived carbon. D